Find an expression for a magnetic field from a given electric field

In summary, The conversation is about correctly splitting the electric field into its components and computing its curl. One person is stuck at the last step and doesn't know what to do next. The other person explains that the electric field can be represented as a constant vector times a scalar function of the dot product, making it easier to compute the curl using the chain rule. The other person also mentions that there is no need to split the electric field into components.
  • #1
TechieDork
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Homework Statement
Find an expression for a magnetic field B(X,t) from a given electric field in a monochromatic plane wave solution E(X,t) using Maxwell's equations.
Relevant Equations
E(X,t) = εe^i(kX-ωt) , X = (x1,x2,x3) , k = (kx1,kx2,kx3) , ω = c|k| , k·ε = 0
ε is a complex vector
Here this is my attempt :

SSZ.jpg


Reference Textbook : Zangwill's Modern Electrodynamics

I stuck at the last step , I really have no idea what to do next.
 
Last edited:
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  • #2
You have not split [itex]\mathbf{E}[/itex] into its components correctly. The [itex]\mathbf{x}_1[/itex] component of [itex]\mathbf{E}[/itex] should be [itex]\epsilon_1 e^{i(\mathbf{k}\cdot \mathbf{x} - \omega t)} = \epsilon_1 e^{i(k_1x_1 + k_2x_2+k_3x_3 - \omega t)}[/itex], etc.

But you don't need to split this into components.

The electric field depends on [itex]\mathbf{x}[/itex] only through a constant vector times a scalar function of the dot product, so its curl is computed most easily by the chain rule: [tex]
\nabla \times (\mathbf{c}f(\zeta(\mathbf{x}))) = f'(\zeta) ((\nabla \zeta) \times \mathbf{c}).[/tex]
 
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Related to Find an expression for a magnetic field from a given electric field

1. How are electric and magnetic fields related?

Electric and magnetic fields are closely related and are often referred to as electromagnetic fields. This is because they are both components of the electromagnetic force, which is one of the four fundamental forces of nature.

2. What is the expression for the magnetic field from a given electric field?

The expression for the magnetic field from a given electric field is given by the Maxwell-Faraday equation, which states that the curl of the electric field is equal to the negative rate of change of the magnetic field over time.

3. Can the magnetic field be calculated without knowing the electric field?

Yes, the magnetic field can be calculated without knowing the electric field if the current density is known. This is because the magnetic field is directly proportional to the current density.

4. How does the direction of the electric field affect the direction of the magnetic field?

The direction of the electric field does not directly affect the direction of the magnetic field. However, the two fields are always perpendicular to each other and the direction of the magnetic field is determined by the right-hand rule, which states that the direction of the magnetic field is perpendicular to both the electric field and the direction of the current flow.

5. Is there any practical application of finding the expression for the magnetic field from a given electric field?

Yes, there are many practical applications of this concept. For example, it is used in the design of electric motors and generators, as well as in medical imaging techniques such as MRI. It is also important in understanding the behavior of electromagnetic waves, which are used in communication and technology.

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